As a controller for controlling a machine system comprised of a load mechanism such as a table or an arm of a robot in a machine tool, a driving device such as a direct-current motor, an induction motor, a synchronous motor, a linear motor or the like, and a transmission mechanism for connecting the load mechanism with the driving device, a controller having two degrees of freedom is often used, which has a feedback control unit which relies on a command value and an output value of a machine system to perform the control, and a feed forward control unit which relies only on the command value to perform the control. For example, Japanese Patent Application Laid Open No. 06-030578 discloses an exemplary controller having two degrees of freedom.
FIG. 1 is a block diagram illustrating the configuration of a conventional motor controller. The motor controller in FIG. 1 comprises feed forward signal processing circuit 25 and B control circuit 23 for performing a feedback control, and is a controller having two degrees of freedom for controlling machine system 6 which comprises load mechanism 1, transmission mechanism 2, electric motor 3, power converting circuit 4, and actual observing unit 5.
Power converting circuit 4 drives electric motor 3 in response to torque command T applied thereto, and a rotating force of electric motor 3 is transmitted to load mechanism 1 through transmission mechanism 2, thereby operating load mechanism 1. Actual observing unit 5 is rotation detector 4 for detecting a rotational speed ω and a rotation angle θ of electric motor 3.
Feed forward signal processing circuit 25 comprises two-inertia-system simulation circuit 24 in which a system is built through approximation and modeling of machine system 6, and A control circuit 22 which is intended to control this two-inertia-system simulation circuit 24. Two-inertia-system simulation circuit 24 receives torque signal TMr applied from the A control circuit, and performs predetermined functional operations including at least two integrations to provide simulation rotation angle signal θMr and simulation speed signal ωMr. A control circuit 22 generates simulation torque signal TMr applied to two-inertia-system simulation circuit 24 based on commanded rotation angle signal ωref provided from command generator 7 as well as simulation rotation angle signal θMr and simulation speed signal ωMr provided from two-inertia-system simulation circuit 24.
B control circuit 23 comprises a position control circuit (not shown) and a speed control circuit (not shown). The position control circuit calculates and provides a speed command based on a deviation of simulation rotation angle signal θMr from actual rotation angle signal θ detected by actual observing unit 5, while the speed control circuit calculates torque command T based on a deviation of the speed command provided from the position control circuit from actual speed signal ω, and provides torque command T to power converting circuit 4. B control circuit 23 can achieve high speed position control performance with the provision of the position control circuit and speed control circuit as mentioned.
Generally, in a motor controller as described above, the control response varies in high-speed property and stability depending on control parameters set in A control circuit 22, two-inertia-system simulation circuit 24 and the like. Generally, in such a motor controller, the parameters are relatively readily set for its control system when the high-speed property is solely required for the control response, or when the stability is solely required for the control response. Typically, however, such a motor controller is often required to provide both the high-speed property and high stability of the control response. In this event, the control parameters of A control circuit 22 and two-inertia-system simulation circuit 24 must be set to meet the requirements for both the high-speed property and high stability of the control response.
However, such a motor controller implies a problem in that adjustments of the control parameters to meet the requirements for both the high-speed property and high stability for the control response are very difficult and time-consuming work for an operator.
Particularly, in failure of establishment of conditions under which a machine system such as machine system 6 is regarded as an ideal rigid body, for example, when machine system 6 appears to include spring characteristics, two-inertia-system simulation circuit 24, which models machine system 6, is subjected to a fourth or higher order control, so that the motor control must find roots of a quartic equation in order to adjust control parameters of A control circuit 22 and two-inertia-system circuit 24 that meet the requirements for both the high-speed property and high stability of the control response, causing a problem in that the adjustments of these control parameters are made difficult and time-consuming.
As described above, in the motor controller, the control response varies in the high-speed property and stability depending on the control parameters set in control circuits. Generally, in such a motor controller, the control parameters are relatively readily set for its control system when the high-speed property is solely required for the control response, or when the stability is solely required for the control response. Typically, however, such a motor controller is often required to provide both the high-speed property and high stability of the control response. In this event, the control parameters of control circuits must be set to meet the requirements for both the high-speed property and high stability of the control response. However, the conventional motor controller implies a problem in that adjustments of the control parameters to meet the requirements for both the high-speed property and high stability of the control response are very difficult and time-consuming works for the operator.